Wastewater treatment has been and continues to be a matter of great environmental importance, including issues relating to municipal sewage or animal waste streams. Traditionally, organic matter containing excessive biological oxygen demand (BOD) has been treated using microbial action in a manner that separates the organic matter, to form a mass of solids in the form of an activated sludge, from the remainder or water fraction. The treatment problem is decidedly two-fold because the water and the sludge fractions both must be treated to be safely returned to the environment, and the two fractions may contain different impurities to be removed.
Treatment typically involves digestion of the organic material through fermentation of the sludge involving aerobic or anaerobic bacterial action or some combination thereof. These processes are used to reduce or consume the chemical oxygen demand (COD) and biological oxygen demand (BOD) of the material and reduce them to an environmentally safe level in the organic materials. It is also necessary to remove undesirable inorganic materials from the water fraction, which typically contains undesirable quantities of phosphorus and nitrogen compounds including phosphates and nitrates.
Wastewater treated by conventional wastewater treatment systems contains soluble, partially soluble and insoluble material as well as contaminates. Materials in the wastewater may be decomposable, partially decomposable or not decomposable. Wastewater treatment systems are designed to provide controlled decomposition of wastes to reduce pollution, health hazards and offensive odors.
Decomposable and partially decomposable materials are referred to as biodegradable; that is, the material may be biologically broken down, or stabilized by bacterial action. Decomposable material is stabilized in wastewater treatment systems by bacteria, protozoa, and other microorganisms. Bacterial consumption of material, creating energy and reproducing bacterial cells, is the foundation of activated sludge wastewater treatment.
Conventional wastewater treatment systems may include pretreatment, primary treatment, secondary treatment, and advanced treatment. Pretreatment includes screening, comminuting (mechanical cleaning of screens by shredding solids to a size which can pass through screen openings), degritting, and grease and scum removal. Primary treatment includes removal of suspended solids from wastewater by clarification and skimming. This typically involves a tank or channel and the following steps: reducing flow velocity, settling heavier solids, and skimming relatively light solids. Primary treatment may include anaerobic digestion processes, aerobic digestion processes, or a combination thereof. Primary treatment systems typically include sludge collection mechanisms, sludge suction devices, grit removal devices, and sludge dewatering devices to reduce the volume of sludge to be disposed. Secondary treatment systems are typically aerobic systems including an aeration phase and a clarification phase. Secondary treatment systems typically include an aeration tank, an air distribution system, a clarifier, sludge collection mechanisms, and sludge removing devices. Advanced treatment includes further removal of suspended and dissolved organic solids by means including filtration and removal of pathogens and chloroforms by oxidation, chlorination or heating, precipitation of minerals, adsorption, or other methods. In a further process in advanced treatment, the purified liquor from the clarifier is typically filtered and refined through chlorination, oxidation, or heating.
In the activated sludge process of primary or secondary treatment, microorganisms are contained in an activated sludge and mixed with incoming wastewater; the wastewater providing food for the microorganisms whereby more activated sludge is produced. Such mixing is accomplished in an aeration tank or channel. In the aerobic activated sludge process, oxygen is intrinsicly mixed with the activated sludge and the wastewater. The microorganisms convert suspended organic solids into energy, carbon dioxide, water, and additional microorganism cells. The aerobic activated sludge process therefore typically includes mixing of wastewater, activated sludge, and oxygen in an aeration tank; consumption of suspended organic solids by bacteria; settling of activated sludge in a clarifier; returning the activated sludge to the aeration tank for further treatment; removing purified liquor from the clarifier; and removing and disposing of the final, inert sludge.
Existing processes and installations for the treatment of such residential and community wastes have generally been large scale operations having installation costs measured in terms of millions of dollars such as associated with typical municipal treatment plants. There exists a need to provide a compact, low-cost system and method for treating wastewater from residential and community sources. There also exists a need for a portable, modular wastewater system.